This application is based upon and claims priorities of Japanese Patent Application No. 2000-266041, filed Sep. 1, 2000, and No. 2001-168630, filed Jun. 4, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a resist composition and, more particularly, to a negative resist composition capable of being developed with an aqueous basic solution, a process for forming a resist pattern using the resist composition, and a process for manufacturing an electron device.
2. Description of the Related Art
LSI and VLSI have come to be used practically in recent years accompanying the process of higher levels of integration of semiconductor integrated circuits, and the minimum line width of the wiring pattern has reached the submicron order. Consequently, it is become essential to establish hyperfine machining technologies. In the field of lithography, as a means of responding to the above requirements, ultraviolet rays as the exposure light source have changed to far-ultraviolet rays having shorter wavelengths, and at the same time, considerable research has been conducted on improvements in the exposure methods using said far-ultraviolet rays as the exposure source. With this research, in the field of resist materials as well, there is a need to develop materials which combine lower absorption of light at the shorter wavelengths described above, have favorable sensitivity and have high tolerance to dry etching.
Described in more detail, research has been actively conducted on photolithography using a krypton fluoride excimer laser (wavelength: 248 nm, abbreviated as KrF) as a new type of exposure light source in the manufacturing process of semiconductor devices, and practical application has already begun. In addition, a resist composition using a concept referred to as chemical amplification has already been proposed by H. Ito, et al. of the IBM Corporation of the USA as a resist having high sensitivity and high resolution and being compatible with such short wavelength light sources (see, for example, J. M. J. Frechet et al., Proc. Microcircuit Eng., 260 (1982), H. Ito et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86 (1983), H. Ito et al., xe2x80x9cPolymers in Electronicsxe2x80x9d, ACS Symposium Series 242, T. Davidson ed., ACS, 11 (1984), and U.S. Pat. No. 4,491,628 (1985)). As can be easily understood from the above-mentioned references, the basic concept of this type of resist composition is to improve the apparent quantum yield by causing a catalytic reaction within the resist film to thereby increase the sensitivity and resolution of the resist composition.
In looking at the example of a chemically amplified, positive resist in which a photo acid generator (PAG), which has the effect of generating acid by light, is added to poly(t-butoxycarbonyloxystyrene) (t-BOCPVP), on which a broad range of research has been conducted thus far, at the exposed portion of the resist, protective groups in the form of t-BOC groups are deprotected by heating after exposure, namely so-called xe2x80x9cPEB (post-exposure baking)xe2x80x9d, resulting in butene and carbon dioxide. The protonic acid formed during deprotection of t-BOC serves as a catalyst which causes the above-mentioned protective group deprotection reaction to proceed along the chain, thereby resulting in a considerable change in the polarity of the exposed portion. Accordingly, a resist pattern can be formed by selecting an appropriate developer which is able to accommodate the large change in polarity of the exposed portion.
More recently, an argon fluoride excimer laser (wavelength: 193 nm, abbreviated as ArF) having a shorter wavelength was expected to be used as the exposure light source for manufacturing further advanced high-integration semiconductor devices such as 1 GbitDRAM devices. However, a conventionally used phenol resin can not be used as a base resin because it strongly absorbs light at the short wavelength of ArF. It is therefore essential to change the base resin of the resist composition. Thus, there is a pressing need to develop a resist which can be used with short wavelengths.
Heretofore, a positive resist has actively been developed as the chemically amplified resist which can be applied at the wavelength of ArF (see, for example, K. Nozaki et al., Chem. Mater., 6, 1492 (1994), K. Nakano et al., Proc., SPIE, 2195, 194 (1994), R. D. Allen et al., Proc. SPIE, 2438, 474 (1994), Japanese Unexamined Patent Publication (Kokai) No. 9-90637, K. Nozaki et al., Jpn. J. Appl. Phys., 35, L528 (1996), K. Nozaki et al., J. Photopolym. Sci. Technol., 10 (4), 545-550 (1997)). Actually, there were few reports on a single-layer chemically amplified negative resist and almost all of them were reports on a crosslinking type resist. In the crosslinking type resists disclosed in A. Katsuyama et al., Abstracted Papers of Third International Symposium on 193 nm Lithography, 51 (1997), Maeda et al., Collected Preliminary Manuscript No. 2,647 (3a-SC-17) (1997) of the 58th Applied Physical Society, T Naito et al., Proc. SPIE, 3333, 503 (1998), Japanese Unexamined Patent Publication (Kokai) No. 2000-122288, and Japanese Unexamined Patent Publication (Kokai) No. 2000-147769, the molecular weight is enhanced by utilizing the crosslinking reaction of the exposed portion to form a difference in solubility in developer between the exposed portion and the non-exposed portion, and thus patterning is conducted. Therefore, limitations on hyperfine machining technologies, due to swelling of the pattern, could not be avoided.
Also a single-layer chemically amplified negative resist using intramolecular lactonization utilizing a hydroxycarboxylic acid structure (see, for example, Y. Yokoyama et al., J. Photopolym. Sci. Technol., 13 (4), 579 (2000)) and a change in polarity due to pinacol rearrangement) (see, for example, S. Cho et al., Proc. SPIE. 3999, 62 (2000)) has recently been reported. However, the use of intramolecular lactonization causes a problem in which high contrast is not easily obtained because of comparatively small change in polarity, while the use of pinacol rearrangement causes problems such as poor adhesion to the substrate due to fluorine and poor storage stability due to maleic anhydride, and thus single-layer chemically amplified negative resists are still imperfect. Although the present inventors have previously developed a single-layer chemically amplified negative resist using a change in polarity due to the intramolecular protection reaction (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 11-311860 and Japanese Unexamined Patent Publication (Kokai) No. 11-305436), there was a problem that high sensitivity is not easily obtained because of the intramolecular reaction.
A negative resist is required when using a phase-shift mask as a super resolution technology which has recently been researched actively and a mask which projects an optical image and is called a Levenson type mask (expected to be used as a technique to obtain definition at an exposure wavelength or lower), and a negative resist is also strongly required in the case of ArF exposure. It is considered that these masks are applied when a definition of 130 nm or lower is required using ArF as a light source. Thus, there is currently a pressing need to develop a resist which can be used without causing swelling.
In order to solve the technical problems of the prior art as described above, an object of the present invention is to provide a novel negative resist composition which allows the use of an aqueous basic solution as the developer and is capable of forming a hyperfine pattern which has a sensitivity suited for practical use and is free from swelling.
Another object of the present invention is to provide a novel resist composition which can be exposed in the deep ultraviolet wavelength region as in the case of a KrF or ArF excimer laser and also has excellent resistance to dry etching.
A still another object of the present invention is to provide a novel resist composition which is capable of forming a hyperfine pattern having both high sensitivity, high contrast and high resolution by enhancing a difference in polarity between the exposed portion and the non-exposed portion.
A further object of the present invention is to provide a useful process using the resist composition of the present invention.
A still further object of the present invention is to provide a process for forming a resist pattern using the resist composition of the present invention.
Another object of the present invention is to provide a process for manufacturing various electronic devices, including semiconductor devices such as LSICs or VLSICs and magnetic recording heads such as MR heads, using the resist composition of the present invention.
These and other objects of the present invention will be apparent from the following detailed description.
As a result of earnest research to solve the above-mentioned problems, the present inventors have found that it is important to use, as a base resin, a film-forming polymer which has an alkali-soluble group and is soluble in an aqueous basic solution, and use a vinyl ether structure protected with an acetal in combination with the film-forming polymer in a chemically amplified resist composition.
The present invention provides a negative resist composition comprising at least a constituent component which has a vinyl ether structure protected with an acetal (acetal-protected vinyl ether structure) in its molecule.
In the negative resist composition of the present invention, the constituent component having an acetal-protected vinyl ether structure can take various forms, but is preferably a film-forming polymer which is soluble in an aqueous basic solution and has an alkali-soluble group, and which contains the acetal-protected vinyl ether structure in the side chain thereof. In such a case, the negative resist composition of the present invention preferably comprises a film-forming polymer and a photo acid generator capable of generating an acid which can react with the alkali-soluble group after the acetal-protected vinyl ether structure produces the deacetalization reaction when decomposed as a result of absorption of imaging radiation, and the negative resist composition itself is soluble in an aqueous basic solution and the exposed portion becomes insoluble in an alkali after exposure.
The constituent component having an acetal-protected vinyl ether structure may be a compound containing the acetal-protected vinyl ether structure in its molecule. In such a case, the negative resist composition of the present invention preferably comprises a combination of the compound containing an acetal-protected vinyl ether structure and a photo acid generator capable of generating an acid which can react with the alkali-soluble group after the acetal-protected vinyl ether structure produces the deacetalization reaction when decomposed as a result of absorption of imaging radiation, and the negative resist composition itself is soluble in an aqueous basic solution and the exposed portion becomes insoluble in an alkali after exposure.
The present invention also provides a process, for forming a resist pattern, which comprises the following steps of:
applying the negative resist composition of the present invention on a to-be-treated substrate;
selectively exposing the formed resist film to imaging radiation capable of provoking decomposition of a photo acid generator of the resist composition, and
developing the exposed resist film with an aqueous basic solution.
The present invention also provides a process for manufacturing an electronic device, which comprises the step of selectively removing an underlying to-be-treated substrate using a resist pattern, formed from the negative resist composition of the present invention, as a masking means to form a predetermined functional element layer. As used herein, the term xe2x80x9cfunctional element layerxe2x80x9d means those contained in the electronic device as a constituent feature and refers to an arbitrary patterned layer and others capable of contributing to the production of a function of the electron device, as described in detail below.
The process for manufacturing the electron device of the present invention preferably comprises the following steps of:
applying the negative resist composition on a to-be-treated substrate;
selectively exposing the formed resist film to imaging radiation capable of provoking decomposition of a photo acid generator of the resist composition,
developing the exposed resist film with an aqueous basic solution to form a resist pattern; and
selectively removing the underlying to-be-treated substrate by etching using the resist pattern as a masking means to form a predetermined functional element layer.
Furthermore, in the process for forming a resist pattern and the process for manufacturing an electron device according to the present invention, the exposure step in the formation of the resist pattern is preferably carried out through a phase shift mask.